1. Field of the Invention
The present invention relates to a cross-linked polyurethane resin powder, or a recycled product resulting from a hard or semi-hard polyurethane resin, and a process for producing the same.
2. Description of the Related Art
As the global environment has been deteriorating, it has been required recently to construct an environment-friendly society. In order to reduce detrimental loads to the environment and to utilize the resources effectively, resin scraps have been investigated for the re-usage.
In the automobile industry, a variety of investigations have been conducted to recycle resin scraps. In particular, resin bumpers are a large-sized component part, and have been investigated extensively to recycle the constituent materials.
Whereas, polypropylene resins and polyurethane resins are used to make resin bumpers. The former resins are thermoplastic resin which can be re-melted, and can be readily recycled by re-molding resin bumper scraps. On the contrary, the later resins are thermosetting resin which forms insoluble and infusible molecular skeletons by cross-linking reactions, and accordingly cannot be recycled without subjecting them to certain preliminary treatments.
The following processes are available to recycle polyurethane resin bumpers: namely;
chemical recycling in which the resin components are decomposed and turned back into original raw materials by chemical treatments, such as glycolysis, aminolysis and hydrolysis; PA1 thermal recycling in which the resin components are burned and collected as a thermal energy; and PA1 material recycling in which the resin components are cut, broken or pulverized, the resulting minute pieces are used as packings, fillers, leveling materials, noise-absorbers or anti-vibrators. Alternatively, the resultant minute pieces are compression-molded by a predetermined pressure to substitute for rubber component parts. PA1 a powder including particles made from at least one resin selected from the group consisting of a hard polyurethane resin and a semi-hard polyurethane resin; PA1 the particles having a superficial portion and an internal portion disposed inside the superficial portion, and involving cross-linked bondings therein; PA1 part of the cross-linked bondings being unchanged, and another part thereof being broken to result in activated groups; and PA1 at least part of the activated groups exposed on the superficial portion of the particles. PA1 hydrolyzing at least one resin selected from the group consisting of a hard polyurethane resin and a semi-hard polyurethane resin in the presence of water and in a temperature range of from a hydrolysis temperature of the resin to a liquefying temperature thereof; and PA1 shearing the resin by applying a predetermined shearing force to the resin, thereby pulverizing the resin.
Especially, in the material recycling, when a recycled component part is prepared by adding scrapped polyurethane bumpers to a virgin resin, it is important to increase the miscibility of the scrapped polyurethane bumpers and the virgin resin in order to inhibit the problems, for example, deteriorated physical properties and degraded superficial appearance, which result from the improperly dispersed scrapped polyurethane bumpers. Hence, it is needed to finely pulverize the scrapped polyurethane bumpers to increase the miscibility of the scrapped polyurethane bumpers and the virgin resin.
It is possible to think of pulverizing a hardened polyurethane resin with a hammer mill, or the like, to prepare a powder. However, this pulverizing process is associated with the problem in that the resultant powder melts together and solidifies by the heat generated from the resin. If the resin is frozen and pulverized in order to suppress the heat generation, such a process pushes up the recycling cost.
Japanese Unexamined Patent Publication (KOKAI) No. 50-154,379 discloses a process for preparing a polyurethane resin powder. In the process, a scrap polyurethane foam is hardened by using a curing resin, and is thereafter pulverized to a powder. Similarly, Japanese Unexamined Patent Publication (KOKAI) No. 51-87,583 sets forth a process for producing fine particles in which a polyurethane foam is swelled by a solvent and is pulverized to fine particles by using a mechanical shearing force only.
Moreover, Japanese Unexamined Patent Publication (KOKAI) No. 6-91,650 discloses a process for finely pulverizing a soft polyurethane foam by using a shearing force of an extruder only. In addition, Japanese Examined Patent Publication (KOKOKU) No. 58-20,969 discloses a process for recycling a polyurethane foam in which water is added to a polyurethane foam, and in which heat and a shearing force are applied to the resulting mixture to thermally plasticize the polyurethane foam. In this technique, the polyurethane foam comprises a linear polymer, and a bi-functional component, such as isocyanate. Therefore, the resultant cross-linked and thermally-plasticized polyurethane foam is a recycled product of low cross-linking density, because, in the thermal plasticization, the main reaction is a chain-developing reaction, and the side reaction is a cross-linking and networking reaction.
On the other hand, in the preparation of a semi-hard or hard polyurethane resin, the chain-developing reaction, and the cross-linking and networking reaction are competitive reactions to each other, because the preparation employs a primary amine as a cross-linking agent. Accordingly, the semi-hard or hard polyurethane resin is a raw material of high cross-linking density, and, in addition to the urethane bondings, it has many urea bondings working as cross-linking points.
In short, the polyurethane resin foam, and the semi-hard or hard polyurethane resin fundamentally differ in the resinous composition. Therefore, even if the polyurethane-foam recycling processes are applied to the semi-hard or hard polyurethane resin, no similar recycled products can be obtained.
As having discussed so far, in order to re-use bumper scraps made from a semi-hard or hard polyurethane resin in a large quantity, for example, by means of material recycling, it is an engineering requirement to establish a technique which can economically prepare a resin powder of stable quality.